Update PushoverHandler.php

... so all available parameters from the (API)[https://pushover.net/api] can be included in the record.
Update PushoverHandler.php

.. according to the feedback @stof gave
Update PushoverHandler.php

... with extra parameters for when the priority = 2

https://pushover.net/api#priority
Update PushoverHandler.php
Merge remote-tracking branch 'Rvanlaak/patch-1'
Remove unnecessary ctor init, refs #446